Measure battery life?

I seem to remember some people mentioning a way to measure the actual battery life obtained on an iBook or PB using some software (not a stopwatch! ). Is there anything out there that essentially runs a timer? Ideally it would be able to tell time spent with computer sleeping and/or only count time when the computer is awake. I'm starting to use my iBook G4 12" on battery more, and I seem to be getting around four hours, but its hard for me to tell for sure because I put it to sleep several times during the day. It'd be neat, just for fun, to know exactly how long its running on battery power.

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